Microbubble entrainment on inclined thin liquid films during drop impact.

Drop impact causes air entrainment between the drop and solid substrate due to a large increase in the pressure underneath the drop, which distorts the bottom interface, creating a thin gas film O(10 nm – 1 μm).We propose that the creation of a central disc of air generates microbubbles while the air escapes. In this study, we report new experimental results on drop impact on an immiscible thin film to show the dynamics of microbubble entrainment. Using high speed imaging, we visualized the formation of the microbubbles across various surface inclination angles and normalized Weber numbers (0 ≤ θ ≤ 75; 5.6 ≤ We_n ≤ 112). We found that with increasing inclination angle, the microbubbles appear even at high We numbers, We_n ~ 112, and that the area of microbubbles nonmonotonically increases then decreases at an optimum We.